Stabilization of nylon rope



ug- 14, 1962 D. HIMMELFARB ETAL 3,048,963

STABILIZATION OF NYLON ROPE Filed NOV. 25, 1960 f/as muera/@QL 50m/V65 3,048,953 Patented Aug. 14, 1962 lire Mass.

Filed Nov. 25, 1960, Ser. No. 71,841 Claims. (Cl. 57-140) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a simple and practical method of making a dirnensionally stable stranded rope, particularly of man-made bers such as nylon, and the product of such method.

It has lbeen recognized that ordinary ropes will shrink when wet, and various procedures have been ofered for reducing this shrinkage. For ropes made of natural fibers, water repellent treatments of the rope and its fibers have been proposed in an effort to make such ropes shrink resistant. Commercial manufacturers stabilize nylon and other man-made thermoplastic ropes by heatsetting them, i.e., subjecting the ropes or their component parts to steam, hot water, or hot air to preshrink and stabilize the rope structure and thereby try to avoid further shrinkage in service. Such procedures have not been entirely satisfactory because of uncertain controls, dubious quality of the product, expensive steam or other heating equipment. The product often gave poor performance in service, and had strand and rope structural deformation, and underwent continual hardening.

We have found that the heat treatment of nylon rope to inhibit shrinkage thereof releases a contractive force of about 0.4 gram per denier resulting in excessive liber shrinkage which induces locked stresses in the rope structure, also that such heat treated nylon ropes continue to shrink -While in storage to the point where they can no longer be uncoiled readily. For example, we have found that some heat treated nylon ropes after two years storage had an increase in hardness or stiffness of about ten times, while the strength of such rope had decreased about thereby corroborating the existence of locked stresses in the nylon fibers of heat-treated nylon ropes. The nylon fibers had also changed shape `from circular to polygonal shape in cross section. For these reasons, heat-treatments are precluded by U.S. lMilitary Specification MIL-R-l7343B from use on nylon ropes. In subsequent wetting in service, heat treated nylon ropes experience not only further rope shrinkage, but the locked stresses therein resulting `from the heat treatment enhance the strand cockling and other undesirable deformations detracting from the serviceability of the rope.

An object of the invention is to provide a relatively simple, economical, practical, convenient, rapid and inexpensive method of making dimensionally and structurally stable rope, particularly from filaments such as nylon, which may be performed at room temperatures and without special heating devices, which requires a minimum of additional apparatus beyond existing ropemaking apparatus, which requires no additional handling of material, which affords no delays in the final processing, which requires no added expensive equipment, with which agents to improve the physical properties or characterstics of the rope may be easily applied to the components of the rope as a part of this process, which is resistant to shrinkage when wet in service, and which provides adequate dimensional stability in nylon rope without stiifening of the rope, its loss of strength when wet, and without the likelihood of strand cockling or rope kinking in service.

A further object of the invention is to provide an improved method of making nylon rope which aifords in such rope controlled relaxation, and a reduction in stresses that would result in objectionable service deformation.

Another object is to obtain an improved and superior, dirnensionally stable nylon rope, which in service will be substantially `free .of strand cockling and other undesirable deformations that detract from the serviceability of the rope; which is free `of locked stresses in the bers or filaments, which, during storage, does not lose strength, or increase in hardness or stiffness, or change shape in the filaments and which will be relatively durable, practical and inexpensive.

Other objects and advantages will `be apparent from the following description of an example of the invention, and the novel features will be particularly pointed out in connection with the appended claims.

In the accompanying drawings:

FIG. 1 is a schematic diagram illustrating an initial step in the method;

FIG. 2 is a schematic diagram illustrating another and subsequent step in the method;

FIG. 3 is a schematic diagram illustrating a further and subsequent step in the method, in which a plurality of cords are formed into strands; and

FIG. 4 is a schematic diagram illustrating another and subsequent step in the method, in which a plurality of strands are assembled and twisted to make a rope.

In the illustrated example of the invention, a plurality of groups of high tenacity, predrawn nylon filaments 11 are employed, and the filaments of each group are twisted together in the usual manner progressively along the group to provide a plurality of yarns 13. A plurality of these yarns 13, such as the three shown in FIG. 2, are twisted together in a direction reverse to the direction of twist in the yarns to form a structurally balanced cord 14, as shown in FIG. 2.

A plurality of such cords 14 are passed through a compression tube 15 in which the cords are compacted and twisted together under some tension in such tube to form a strand 16, with the direction of twist opposite from the direction of twist in the cords. The bore of the tube 15 is adjusted according to the size of the rope, ranging for example, from 0.109 inch for inch circumference rope strand to 1.281 inches for the 8 inch circumference rope strand. The cords 14 are wet long enough before they pass into and through the compression tube 15, and with suiiicient aqueous liquid, to render them plastic ybefore they `reach the tube 15. The wetting, preferably to saturation, may be caused in any suitable manner such as `by passing each cord through a body of the aqueous liquid, or as shown, by way of example, fby spraying the cords with the aqueous liquid from one or more spray nozzles 17 which are supplied with the aqueous wetting liquid under pressure. In the passage of the wet and plastic cords through the compression tube, the necessary and usual compressive and tensile forces will prevail. The compacting and twisting of the cords into the strand except for the wetting is according to the usual rope-making practice.

A plurality, such as three or more for example, of the strands 16, the number depending on the desired size of the rope, while still wet or moist are wound on spools or reels 18 and then while in that condition `are passed through a die 19 where they are twisted together into a rope, with the direction of twist opposite or reverse from that in the strands, and while the strands `are under some tension, such as the tension necessary for unrolling them from their bobbins or reels and drawing the strands through the die 19. The rope so formed is then dried while still under some small tension, such as by passing it while still under some tension, through a drying chamber 2li.

spense-s It will be noted that the direction of twist is reversed consecutively at each step from iilament to yarn, yarn to cord, cord to strand, and strand to rope, as usual in the rope-making art, and in addition, there should be a structural balance in the cord twist to obtain the best properties in the final rope structure of which the balanced cords are component members. The balance between the cord and yarn twists at the second stage of twisting is important. To obtain this balance, the filaments or fibers may be twisted into yarns with a helical angle of twist of about to 25, and these yarns, such as three yarns, are twisted in the reverse `direction into a cord, where this degree of twist is measured by lche turns per foot amounting to 70 to 85 percent of the turns per foot of the component yarns, which etects a balance between the opposing torsional forces manifest between the cord and the component yarns.

The problem of structural stability with respect to shrinkage when a rope is exposed to wetting in service has long been characteristic of the rope structure. Ropes made of natural grown fibers of which manila and sisal are examples, swell when exposed to water, and as a con sequence of swelling become considerably more rigid and tend to kink and shrink in length. When subsequently dried out, the rope acquires a loose structure because the action of swelling has displaced the iibers permanently, and due to the locking `efiect of the spirals of the strands, there is no opportunity for the strands or yarn components to return to their original condition. The extent of swelling is considerably more pronounced than the effect of shrinkage. Since swelling tends to be a ber property, subsequent rewetting repeats the swelling, but since the spiral strands retain their relative positions, the rigidity and stiffness noted with the first wetting are retained.

In accordance with this invention where the cords are rendered plastic by wetting with water, then while plastic drawn through the compression tube, and then wound on the bobbin reels, the strands and their component yarns and fibers are under considerable tension and simultaneous compression. The efiect of this is to exercise control over the swelled yarns `and stretch them out while in a plastic condition, thereby stabilizing them in relation to subsequent wetting exposure.

In dimensionally stabilizing such a rope when its component parts contain non-cellulosic man-made filaments, such as nylon and other thermoplastic rope materials, the rope components should be wet, and preferably may be saturated, with the aqueous liquid before they reach the compression tube. While the wetting of the fibers could be done at any stage before reaching the compression tube, there is danger that the wetted fibers may dry and lose their plasticity before reaching tube 15. Hence, it usually is preferable to wet the fibers in the cords somewhat before they reach tube l5. The strands are wound on bobbins 18, and then these bobbins are mounted to feed the strands while still plastic to the usual die 19 in which the strands are twisted together while under some tension to form the rope as usual in rope making. The rope is then dried under some tension such as by passing it from the die 19 through the oven 20 by the tension of drawing the rope through the die 19".

The aqueous wetting agent can also be used `as a convenient medium for incorporating in the rope one or more agents for imparting desired physical properties or characteristics to lthe rope. For example, to the aqueous liquid one may add an agent to improve lubricity, an ant-istatic electricity agent, a water dispersible or soluble agent, a dye, a color, a resin or an agent to improve the wet strength of the rope. The twisting together of the various components of `the rope may be performed on the conventional rope-making machines, using the compression and tensile forces normal to the rope twisting operations after the filaments have been swelled and remain plastic while subject to these forces. The wetting of the components of the rope prior to the completion of the rope controls subsequent shrinkage of the rope. The twisting of the components of the rope under tension when wet, tends to stretch and closely pack the fibers and hence, inherently function mechanically to limit subsequent shrinkage. With this procedure, no after treatment of the rope is required. The aqueous wetting liquid need not be heated, and may be at about room temperatures or may even be relatively cold, so that the stabilization is not accomplished by heat setting or by hot water applied to the rope or its components.

The present invention is particularly applicable and advantageous in dimensionally stabilizing rope made of predrawn, high tenacity nylon filaments, rather than rope made of rayon, wool, and cellulosic ibers. The wetting changes the nylon yarns into a plastic condition, so that when they are Compressed and held simultaneously in tension, the plastic condition of the yarns allows more stretch thereby eliminating some residual stretch, provides better compacting of the filaments, yarns, cords and strands, and by virtue of the locking effect of surrounding spiralling yarns, maintains the pre-stretched condition when strands are laid into rope. The pre-wetting operation requires less twist to attain a given state of compacting, which decreases the elastic response in the finished rope structure. The objective in the manufacture of nylon rope is to reduce, rather than enhance the elongation. Yhe present invention precludes the necessity of heat in any form as a factor in the control of shrinkage of the rope. The control of physical form, such as yarn setting or liveliness, for subsequent operation is not a factor in the application of this invention. No special tensioning equipment is required to attain high relative stretch in the twisted structure. Here the idea is to compact and reduce stretchability in the rope, rather than stretch the rope components, using cold or unheated water or water at room temperatures to plasticize and preshrink the rope components. No complicated or expensive additional apparatus is required to obtain the desired results. It is believed to be new, the making of a preshrunk nylon rope from predrawn, high tenacity nylon filaments using concurrent compression and twisting in the strand-forming tube under the tension used with the twisting operation normal to the rope-making process, to obtain a rope structure of higher strength, lighter weight, and reduced stretch. Nylon ropes made according to this invention have been found to be superior in performance to nylon ropes made without the prewetting. Not only is the adverse effect of wetting minimized in shrinkage, but also in high-tensile loading service there is manifested no structural deformation, such as strand cockling and rope kinking. Microscopic studies under polarized light of nylon rope made in accordance with this invention have shown that the filaments were entirely free of locked stresses and retained their circular cross-sectional shape. Prior nylon ropes not made in accordance with this invention will undergo considerable shrinkagel when wet in service, resulting in stiliening of structure and inducement of strand cockling and other undesirable rope deformation.

Many details of rope-making employed by applicants and which are conventional or common in the art have been omitted herein as far as possible, in order to simplify the description, but for full information on such omitted details, reference may be had to a book The Technology of Cordage Fibres and Rope by applicant, D. Himmelfarb, and published in 1957 by Leonard Hill (Books) Ltd., London, England, Interscience Publishers of New York City, New York, agent in the United States.

An important feature of this invention is that the rope is made of filaments of predrawn, high tenacity nylon in contrast to the use of undrawn nylon fibers which have different physical properties. Undrawn iiber or filaments such as extruded filaments resemble nylon fiber in plastic form. Generally the more extensively the nylon fiber or filament is drawn, the greater its tensile strength, but the less its ability to stretch. Drawn nylon bers or filaments have greater tensile strength but less stretchability than undrawn fibers or filaments. This is explained in the book Technology of Synthetic Fibers, edited by S. B. Mc- Farlane, Fairchild Publications, New York, New York (1953), pages 104 and 105 where it is stated:

The physical properties of the drawn tiber are a function of the draw ratio as is shown in FIGURE 3. By draw ratio is meant the ratio of drawn length (prior to relaxation) to initial length of the yarn. You will note that a draw ratio of 2.51 gave a yarn with a tenacity (strength) of 2.2 g./d. and an elongation of 160%. By increasing the draw ratio to 5.38, which is about the limit of cold drawing for this yarn, the tenacity was increased to 6.6 g./d. and elongation was decreased to 22% Orientation favors close packing of the chains and the formation of crystallites. This lowers moisture absorption It is believed that these properties stem directly from the length of the chain (of the order of 100 monomer units).

FIGURE 3 "Physical Properties as a Function of Draw Ratio" Moisture, Draw ratio Tempera- Tenacity, Elongation, 78 F., 72%

ture of g./d. percent RH.,

Drawing percent 2. Cold l 2. 2 1 160 4. 67 3. Cold 3. l 89 4. 52 4. Cold 4. 6 50 4. 29 5. Cold 5.8 36 3. 90 5. Cold 6. 6 22 3. 75 6. Hot 8.2 21 3.54

1 Suter tester.

The drawn nylon fiber which is used by applicants corresponds to the nylon obtained with a draw ratio of 5.3 8. U.S. Government speciiications for lnylon rope require the rope to be made of drawn nylon tibers. There are major differences in physical properties lbetween ropes made of undrawn and drawn fibers and filaments, and such differences extend to the properties of strength and wetting shrinkage, these properties being attributes of the extent of the drawing of the nylon ber or filament used in the making of rope. There are established differences between undrawn nylon ber rope and predrawn nylon liber rope, with respect to the etfect of water soaking. The undrawn nylon iiber rope when wet will not materially change the permanent properties of the nylon, but a rope made of predrawn, high-tenacity nylon fiber, when wet has a definite shrinkage, changing the elongation properties of the rope as well as the breaking strength according to the following quantitative test data, obtained by testing nylon rope made of high tenacity predrawn nylon laments:

Drawn Nylon Fiber Rope Size (Circumfercnce) (inches) 1% 2% 3% Shrinkage Attaiued By Cold Water Soaking,

percent 6.9 7. 5 9. 1 Percentage Stretch to the Breaking Point:

Rope Dry, before Water Soaking, percent. 52. 5 40. 4 41.3 Rope Dry, after Water Soaking, percent 5S. 3 50.0 56. 7 Breaking Strength (lbs):

Rope Dry, before Water Soaking 7, 100 18, 600 30,000 Rope Dry, after Water Soaking 6, 600 16, 800 26, 400

These quantltative measurements illustrate that the adsional and handling characteristics according to the following quantitative test data on ropes made of high tenacity, drawn nylon filaments.

These changes are permanent effects, with respect to subsequent water soaking and drying. A rope made in accordance with this invention has stabilized characteristics, in service, such as of constant length, high strength, minimum stretch, and structural compactness without deformation, which determine optimum serviceability. Rope made of undrawn nylon fiber has retention of maximum elongation, the opposite of shrinkage. The test results above given establish that the cold water treatment of rope made of high tenacity, predrawn nylon larnents did more than provide a lubricant in a drawing operation, and that by it positive characteristics were imparted to the rope by applicants method. The changes associated with wetting drawn nylon bers become extensively magnied when the iibers are twisted together and converted to the heavier rope structure. Freedom for reversible movements of fiber elements in rope, which are associated with wetting and drying of the rope, become restrained by the multiplicity and mutual compression of the bers. Hence, manifestations of structural changes due to wetting of a nylon rope become more apparent. The step in applicants method of creating the structural balance in the cord, during the twisting of the yarns of drawn, high tenacity nylon filaments into the cord, contributes to the success of applicants method by allowing the controlled shrinkage to occur without deformation ofI the rope structure.

This application is a continuation-in-part of our copending application for patent, Serial No. 818,490, tiled June 5, 1959, now abandoned.

It will be understood that various changes in the details, steps, materials, operating conditions and apparatus, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

We claim:

l. The method of making a shrinkage-stabilized nylon rope which comprises twisting a plurality of filaments of predrawn, high tenacity nylon into yarns, twisting a plurality of such yarns into a structurally balanced cord, twisting a plurality of such cords into a strand with transverse compression and compacting during such twisting, twisting a plurality of such strands into a rope, and during the twistings, wetting with an unheated aqueous liquid, at least one of said filaments, yarns, cords and strands to render them somewhat plastic and continuing the subsequent twistings while the wetted components are still somewhat plastic.

2. The method of making a shrinkage-stabilized nylon rope which comprises twisting a plurality of laments of predrawn, high tenacity nylon into yarns, twisting a plurality of such yarns into a structurally balanced cord, twisting a plurality of such cords into a strand with transverse compression and compacting during such twisting, twisting a plurality of such strands into a rope, and prior to the tinal twisting wetting the components of such rope with an aqueous liquid suiciently to render such components somewhat plastic.

3. The method according to claim 2, wherein said wetting is heavy enough to cause saturation of such components.

4. The method according to claim 2, wherein said aqueous wetting liquid has intermiXed the-rein a liquid which modifies the physical properties of the rope components. 5. The method according to claim 2, wherein said aqueous liquid also carries in it an added lubricating agent.

6. The method according to claim 2, wherein said aqueous liquid has intermiXed therein an anti-static agent.

7. The method of making a dimensionally stable rope from predrawn, high tenacity nylon, which is free from stitiening in storage and when wet and also from loss in strength when wet, which comprises twisting under some tension aV plurality of filaments of said nylon into a rope through successive stages, employing reverse twist in successive stages, of yarns, cords, strands and ending in said rope, with the cords compacted together sidewise during their twisting into strands, and wetting the nylon with suicient aqueous liquid not materially above room ternperature to render the nylon somewhat plastic prior to the iinal twisting of strands into rope, and drying the rope so formed under some lengthwise tension at a temperature well below that which would heat set the nylon.

S. The method according to claim 7, wherein the wetting is suicient to amount to saturation.

9. The method according to claim 7, wherein said wetting is of the cords, and the subsequent twisting stages are performed while the nylon is still somewhat plastic.

l0. The method according to claim 7, wherein said strands are compacted together sidewise during their twisting into a rope.

11. The method according to `claim 7, wherein said twist of yarns into cords provides a structural balance in the cords.

12. A dimensionally stable nylon rope formed of predrawn, high tenacity nylon filaments twisted together into yarns, said yarns intertwisted into cords, said cords intertwisted and compacted sidewise into strands, and `said strands intertwisted and compacted sidewise into said rope, with the twist successively in reverse directions in said yarns, cords, strands and rope, sa-id rope being substantially free from stiening in storage and when' wet in service, having minimum loss in strength when wet in service, substantially free of locked stresses, `strand cockling, rope kinking and structural deformation, and having` the filaments in substantially their original cross-sectional shape.

13. The method of making a non-kinking nylon rope which is resistant to lengthwise shrinkage when Wet in service, which comprises intertwisting into a yarn a plurality of filaments o-predrawn, high tenacity nylon, intertwisting a plurality of such yarns into cords, intertwisting a plurality of such cords into strands while concurrently passing them through a compression tube, intertwisting a plurality of such strands into a rope while `concurrently passing them through a die and, prior to such twisting of such strands into a rope, wetting the nylon components of which the rope is formed with sufiicient aqueous liqiud to render the iilaments plastic before they reach the compression tube and iinal twisting operation, and drying said rope under some tension at al temperature well below that which would heat set the nylon.

14. A nylon rope comprising a plurality of yarns of intertwisted high tenacity, predrawn nylon iilaments, intertwisted with one another into a cord, a plurality of such cords intertwisted with another in stretched and closely compacted condition into a strand, and a plnrality of such strands intertwisted with one another into a rope free of locked stresses, having a structural balance between the cord and yarn twists at the second stage of such twisting, stabilized in length in relation to subsequent wetting exposure, and with minimum stiffness, loss of strength when wet, and substantially free of cockling and rope kinking in service.

15. The method of making a shrinkage-stabilized nylon rope which comprises twisting a plurality of laments of predrawn, high tenacity nylon into a yarn, twisting a plurality of such yarns into a structurally balanced cord, twisting a plurality of such cords into a strand with concurrent transverse compression and compacting during such twisting, twisting and passing a plurality of such strands through a die into a rope under tension, and prior to said twisting of the cords into a strand, wetting said cords thoroughly with water, and drying the rope so formed while under tension.

References Cited in the le of this patent UNITED STATES PATENTS 2,028,158 Hodson Jan. 2,1, 1936 2,407,105 eymour et al. Sept. 6, 1946 2,799,133 Rose July 16, 1957 2,971,321 Hirnnielfarb et al. Feb. 14, 1961 FOREIGN PATENTS 543,974 Great Britain Mar. 23, 1942 OTHER REFERENCES Handbook of Chemistry and Physics, 35th edition; page 1459, published by Chemical Rubber Publishing Co., 231i() Superior Avenue NE., Cleveland, Ohio.

Harris Handbook of Textile Fibers, first edition, 1954; pages 104, 105, 2021, 232, published by Harris Research Laboratories, Inc., 1246 Taylor Street NW., Washington 11, D.C. 

